Fuel injection valve

ABSTRACT

A fuel injection valve for fuel injection systems of internal combustion engines, includes components that can be manufactured in an inexpensive and simple manner. The valve needle movable along a longitudinal valve axis is formed by a thin wire, which represents the downstream elongated extension of a helical restoring spring. The valve needle engages in a sealing element, which is coupled to a valve seat body having a fixed valve seat. The valve needle and the sealing element are arranged with respect to the valve seat so that the wire transmits pressure forces to the sealing element in the closed position. The fuel injection valve is suited for use in fuel injection systems of compressed mixture, externally ignited internal combustion engines.

BACKGROUND INFORMATION

German Patent Application No. 25 08 390 describes a fuel injection valvehaving an axially movable valve needle designed as a thin rigid rod oras a non-rigid wire. The downstream end of the rod is connected byfriction to a closing head, which works together with a valve seat. Onits opposite end, the rod runs through an armature and is connected to atension spring upstream from the armature. The tension spring isresponsible for the closing head being drawn to the valve seat via therod when the magnet coil is not energized, so that the valve is in theclosed position. If the magnet coil is energized, it attracts thearmature, and the tension spring is extended. As a result, the rod movesaxially so that the closing head rises from the valve seat. The tensileforces of the tension spring cause the valve to reclose when the magnetcoil is not energized.

German Patent Application Nos. 34 27 526 and 35 35 438 describeelectromagnetically actuated fuel injection valves having a flatarmature in their magnetic circuit, German Patent Application No. 34 27526 also describes a light and elongated valve needle.

SUMMARY OF THE INVENTION

The fuel injection valve according to the present invention has theadvantage that it can be manufactured with simple and inexpensivecomponents. The valve needle is designed as a thin wire, connected to asealing element, and the sealing element is in turn coupled to a valveseat. It is advantageous that the valve needle and the sealing elementmay be designed so that the wire transfers pressure forces to thesealing element and the valve seat in the closed valve position, i.e.,when the sealing element is in contact with the valve seat.

It is advantageous to design the wire used as a valve needle in onepiece as an elongated downstream extension of a helical restoringspring, the elastic force of which brings the sealing element into theclosed valve position through the valve needle. In order to increase theflexural strength of the thin wire, the valve needle is advantageouslyprovided with a support element, which can be manufactured in a simplemanner. A very high degree of flexural strength is achieved with minimumadditional weight through an L-shaped sheet metal angle partiallysurrounding the elastic wire located in the bend of the sheet metalangle. The two legs of the support element prevent the sheet metal anglefrom slipping on the wire.

It is also advantageous for a non-positive bond to be between the wireand the sealing element. The wire, rounded on its downstream end,engages in a depression of the sealing element and thus transfers thepressure forces of the restoring spring to the sealing element. It isadvantageous if the depression has a conical shape with the bottom ofthe depression ideally having the same diameter as the rounded wire end.

In addition, it is advantageous if an armature of the electromagneticcircuit is designed as a flat armature, which supports the restoringspring. Due to its small height, a flat armature design is particularlyrecommended- The design of a flat armature allows a non-magnetic, forexample, austenitic, material to be used for a valve seat support, whichcan be deep-drawn much better than a ferritic material, resulting inlower production costs.

With the fuel injection valve according to the present invention,injection points can be preset to a considerable degree (e.g., as earlyas in the intake pipe) in a simple manner (extended tip injector), sincethe lengths of the deep-drawn valve seat support and the elastic wirecan be easily and inexpensively varied. It is of great advantage that inthe above-mentioned design of the valve needle the preset injectionpoint can be achieved with a very small moving mass.

In order to guarantee that the injection valve opens when the magnetcoil is energized, an elastic corrugated disk is arranged between thesealing element and a valve seat body which features the valve seat andis coupled to the sealing element; the elastic force of the corrugateddisk opposes the elastic force of the restoring spring. Thus the sealingelement is raised from the valve seat by the corrugated disk. Thecorrugated disk advantageously has bore holes, slots, or grooves toallow the fuel to flow in the direction of the valve seat. In addition,the corrugated disk is responsible for the radial guidance of thesealing element in the valve seat support.

The valve seat body may also have a conical orifice, in which an atleast partially conical self-centering perforated disk can be inserted.Thus expensive centering devices are not required for the assembly ofthe perforated disk.

The design of the armature and the valve seat body as a flat armatureand a flat seat allows relatively great guidance tolerances, whichreduces manufacturing costs.

These above-mentioned overall design features, making welding operationson the sealing element and the valve seat body unnecessary, allowceramic to be used for these two components, for example, whenaggressive fuels are used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fuel injection valve with a valve needle according to anexemplary embodiment of the present invention.

FIG. 2 shows a section along a line II—II in FIG. 1.

FIG. 3 shows an enlarged view of a downstream end area of the fuelinjection valve of FIG. 1.

DETAILED DESCRIPTION

An exemplary electromagnetically actuated valve in the form of aninjection valve for fuel injection systems for compressed-mixture,externally ignited internal combustion engines, illustrated in FIG. 1,has a tubular core 2 serving as a fuel inlet fitting, surrounded by amagnet coil 1; The tubular core has stepped inner and outer diametersover its axial length, for example. A bobbin 3 made of plastic receivesa winding of magnet coil 1 and allows, in conjunction with core 2, acompact design of the injection valve in the area of magnet coil 1.

Core 2, concentric with a longitudinal valve axis 10, has, in thecentral area of its axial length, a shoulder 11 on its external contour;on this shoulder, core 2 is connected to a metallic valve jacket 12 bylaser welding, for example. Valve jacket 12 has a stepped design, sothat it extends radially outward above magnet coil 1 from core 2 with anarea 13, and then surrounds magnet coil 1 from the outside, viewed inthe downstream direction. Thus magnet coil 1 is embedded between core 2and valve jacket 12. In the downstream direction, a sleeve-like valveseat support 16, which may be stepped, follows valve jacket 12 and ispermanently connected to it. A longitudinal orifice 17 runs in valveseat support 16 concentrically with longitudinal valve axis 10. While anupper area 17 a of longitudinal orifice 17 is sufficiently wide tosurround, at least partially, valve jacket 12, a lower area 17 b oflongitudinal orifice 17 has a smaller diameter. A valve needle 18 isarranged mainly in lower area 17 b of longitudinal orifice 17.

The injection valve is actuated in a conventional manner, for example,electromagnetically. Electromagnetic circuit with magnet coil 1, core 2,valve jacket 12, and armature 21 are used to move valve needle 18axially, and thus to open the valve against the elastic force of arestoring spring 20 and to close the injection valve. Armature 21 isdesigned in the shape of a flat armature, connected with its upstreamend to valve needle 18 and aligned with core 2. A cylindrical valve seatbody 23 having a fixed valve seat is mounted in longitudinal orifice 17at the downstream end of valve seat support 16 that faces away from core2.

Core 2, used as an inlet fitting for fuel and a stop for armature 21,has, in the downstream direction from shoulder 11, a smaller outerdiameter than it does upstream from shoulder 11, whereby the injectionvalve also has a relatively small outer diameter in the area of magnetcoil 1. Core 2 is either a turned part or a deep-drawn ferritic tube. Abottom stop surface 25, facing armature 21, is chrome-plated orchemically nickel plated, for example. Valve jacket 12, resembling aguide cup, is a deep-drawn ferromagnetic component. In its radial area13 above magnet coil 1, valve jacket 12 has a recess 26, through whichcontact rods 27, exiting magnet coil 1, are guided. Valve jacket 12 has,on its external contour, below area 13, specially designed sections, forexample —a top section 12 a, which has grooves 28 running in thecircumferential direction to provide positive connection with anextruded plastic part 30, and a bottom section 12 b, with a depressionto fit valve seat support 16. A bottom pole surface 31 of valve jacket12 is also chrome-plated or chemically nickel-plated like stop surface25; both surfaces 25 and 31 are situated in one plane, for example.

Bobbin 3 is responsible for dissipating heat and protecting the windingof magnet coil 1 from damage. Two ring projections extend from bobbin 3in the direction of armature 21, so that three annular chambers 34 areformed between the two ring projections 33 proper and between theinternal ring projection 33 and core 2, and the external ring projection33 and valve jacket 12. A seal ring 35, designed as an o-ring, forexample, is placed in each of the internal and external annular chambers34. With this measure, it is achieved that magnet coil 1 remains dry.Seal rings 35 are axially secured by arranging a supporting ring 36having a T-shaped cross section between magnet coil 1 and armature 21;an axial arm extends into central annular chamber 34 between the tworing projections 33. The radial arms of supporting ring 36 press againstseal rings 35.

Armature 21, designed as a flat armature, is a thin, circular disk,stamped from a larger sheet, for example. A central through hole 38serves to let the fuel flowing from core 2 in the direction of the valveseat through, and to guide an elastic wire 51 of valve needle 18.Outside central through hole 38, additional holes 39 are provided inarmature 21 to achieve a reduction in splash losses due to the flowresistance in the armature area, which would otherwise be too high.Through hole 38 has an embossed recess 40 on the upstream side ofarmature 21; this recess supports restoring spring 20. Like stop surface25 and pole surface 31, the upstream face of armature 21 opposite thesesurfaces is surface coated, for example, chrome-plated or nickel-plated,to provide sufficient wear protection. Valve seat support 16 isprecision fabricated with its internal longitudinal orifice 17 so thatits upper area 17 a provides radial guidance for armature 21.

An adjustment sleeve 43, inserted in a flow bore 42 of core 2,concentric with longitudinal valve axis 10, is used for adjusting theelastic pre-tension of restoring spring 20 in contact with adjustmentsleeve 43; restoring spring 20 is supported by recess 40 of armature 21on its opposite side.

Downstream from armature 21, a disk spring 45 is arranged in thelongitudinal orifice 17 of valve seat support 16; the disk spring holdsarmature 21 in its initial position when the armature is not energized,and has an elastic force action against restoring spring 20. Disk spring45, manufactured by stamping and bending, for example, is provided witha circular outer ring 47 and a circular inner ring 48. Both rings 47 and48 are connected to each other through a plurality of spokes, arrangedover 360°. When magnet coil 1 is energized, disk spring 45 supports theclosing motion of armature 21 against the elastic force of restoringspring 20. In addition, disk spring 45 prevents armature 21 fromwobbling. In addition to guiding armature 21, valve seat support 16provides, with its upper area 17 a, radial guidance for disk spring 45.While the slightly convex outer ring 47 is supported by the bottom faceof armature 21, outside holes 39, inner ring 48 of disk spring 45 is incontact with a radial shoulder 49, running radially between areas 17 aand 17 b, of valve seat support 16. The inner bend radius, facinglongitudinal valve axis 10, between shoulder 49 and bottom area 17 b, iswell suited as a contact area, for example.

Wire 51, in particular elastic wire, serving as valve needle 18,represents the single-piece extension of restoring spring 20, forexample, running in a spiral shape to recess 40 of armature 21 andaxially straight from there in the downstream direction. On itsdownstream end, valve needle 18 is rounded, for example, in order toengage in a central, for example, conical, depression 50 of sealingelement 52. Valve needle 18 transmits the elastic force (pressure force)of restoring spring 20 to sealing element 52. The disk-shaped sealingelement 52 is coupled to valve seat body 23 and forms a seat valve.

To protect the very thin elastic wire 51 from bending, valve needle 18has an additional, angled support element 53, having an L-shaped crosssection. Support element 53 is a sheet bent in a simple manner,surrounding elastic wire 51, in an approximately right angle, over thegreater part of the axial extension of valve needle 18 As FIG. 2 showsas a section along line II—II in FIG. 1, elastic wire 51 is stabilized,for example, by providing it with connecting brackets 54 engaging in thebend of support element 53 and connecting the two legs of supportelement 53. Elastic wire 51 of valve needle 18 can also be permanentlyconnected to support element 53 by welding, soldering, or gluing. Highflexural strength of valve needle 18 is achieved in a simple manner witha support element 53.

Disk-shaped sealing element 52 has, on its bottom face 56 facing valveseat body 23, an outer recess 57, running a full 360°, in which acircular elastic corrugated disk 58 is arranged. Bottom face 56 ofsealing element 52, manufactured from stainless steel or ceramic, forexample, serving as a sealing side together with valve seat body 23, isprecisely machined except in the area of recess 57—lapped, for example.Sealing element 52 is radially guided during its axial movement alonglongitudinal valve axis 10 via corrugated disk 58 in the area 17 b ofvalve seat support 16.

In addition to guiding sealing element 52, corrugated disk 58 has themain function of raising sealing element 52 from valve seat body 23 whenmagnet coil 1 is energized. When magnet coil 1 is not energized, i.e.,the valve is closed, a non-positive bond exists between elastic wire 51and sealing element 52, as well as between sealing element 52 and valveseat body 23 due to the pressure exerted by restoring spring 20, becausethe elastic force is transmitted via valve seat 18 to sealing element52. If magnet coil 1 is energized, armature 21 is drawn against theelastic force of restoring spring 20, valve needle 18 being forced toeffect the same axial movement. This movement of valve needle 18 resultsin elastic wire 51 rising from sealing element 52, while sealing element52 remains on valve seat body 23. Sealing element 52 follows themovement of valve needle 18 due to corrugated disk 58 having an elasticforce acting against the elastic force of restoring spring 20, and thevalve opens when armature 21 is attracted. Corrugated disk 58 canadvantageously receive and store axial forces. For example, a pluralityof orifices, in the form of bore holes, slots, or grooves are providedon corrugated disk 58, through which fuel can flow to valve seat body23.

Sealing element 52 and valve seat body 23 are made of the same material,for example, of stainless steel or ceramic. Valve seat support 16 has onits bottom side 59 a bulge 60 with a larger inner diameter than in area17 b, in which valve seat body 23 is precisely positioned. Valve seatbody 23 may be in contact with another oblique surface 62 of bulge 60serving as a stop. Small depressions are made on the upper face of valvebody 23, facing sealing element 52, so that at least two raised areasare formed: an outer support area 65 and an inner sealing area 66. Bothareas 65 and 66 represent concentric rings, for example, outer supportarea 65 serving as a stop for corrugated disk 58, and inner sealing area66 being directly coupled to bottom face 56 of sealing element 52 as asealing surface. Sealing area 66 is precision machined, for example,lapped, according to the hermeticity requirements of the valve. Acentral cylindrical orifice 68 on the top face of valve seat body 23 isfollowed by an orifice area 69 that widens in the downstream directionin the shape of a truncated cone. The flat armature and flat seat designallow for relatively large guidance tolerances, making manufacturinginexpensive.

On its bottom face facing away from sealing element 52, valve seat body23 is provided with a perforated disk 75, which may be cup-shaped, forexample. Perforated disk 75 nestles mainly to the wall of the conicalorifice area 69, while it has a circumferential flat holding edge 76radially outside orifice area 69. In the area of holding edge 76, thereis a seal ring 77, for example, between valve seat body 23, bulge 60 ofvalve seat support 16, and perforated disk 75, to seal the seat area.Immediately downstream from orifice 68, in a largely flat bottom area ofperforated disk 75 near longitudinal valve axis 10, at least one, butpreferably four, injection orifices 78, formed by erosion or stamping,are provided. The largely conical design within orifice area 69 isadvantageous for perforated disk 75 to be self-centering. The cone angleof perforated disk 75 is approximately 2° smaller than the cone angle oforifice area 69 of valve seat body 23. Perforated disk is fastened, forexample, using a circular ring-shaped downstream support disk 79, whichsecures holding edge 76 of perforated disk 75 between itself and valveseat body 23. By providing a bead on end 59 of bulge 60 below supportdisk 79, perforated disk 75 and support disk 79 are secured in a simpleand reliable manner. It is also possible that the cup-shaped perforateddisk 75 be connected to valve seat body 23 concentrically andpermanently, for example, using a circumferential seal such as a laserwelding seam. FIG. 3 shows an enlarged view of a downstream end area ofthe fuel injection valve of FIG. 1.

Valve seat support 16, which may be deep-drawn, is made of anon-magnetic austenitic material. In area 17 a, valve seat support 16 ispermanently and hermetically connected to valve jacket 12 in thedepressed section 12 b, for example, using a laser welding seam. Thedepth of insertion of valve seat body 23 determines the pre-setting ofthe stroke of valve needle 18. The exact adjustment of the stroke isdetermined by the plastic deformation of radial shoulder 49 of valveseat support 16 in the axial direction. One end position of valve needle18 when magnet coil 1 is not energized is determined by the contact ofsealing element 52 on valve seat body 23, while the other end positionof valve needle 18 when magnet coil 1 is energized results from thecontact of armature 21 with stop surface 25 of core 2.

Upstream from the coil area, the injection valve is surrounded byextruded plastic jacket 30, which encloses most of core 2 and extends inthe axial direction to section 12 a of valve jacket 12, valve jacket 12being partially covered in the axial and circumferential directions. Anelectric connecting plug 82, in which the two contact pins 27 comingfrom magnet coil 1 and serving to energize magnet coil 1 end, isextruded together with this plastic jacket 30.

On the intake-side end of the injection valve, a fuel filter 83protrudes into flow bore hole 42 of core 2. The fuel entering the fuelinjection valve flows through fuel filter 83 in the known manner andexits fuel filter 83 in the radial direction. Fuel filter 83 isresponsible for filtering out particles entrained by the fuel, which dueto their size or chemical composition might clog or damage the injectionvalve.

What is claimed is:
 1. A fuel injection valve for a fuel injectionsystem of an internal combustion engine, comprising: a valve needleincluding a thin wire and being movable along a longitudinal valve axisof the fuel injection valve; a valve seat; an axially movable sealingelement cooperating with the valve seat, wherein the fuel injectionvalve is in a closed position when the axially movable sealing elementis in contact with the valve seat, and wherein, in the closed position,the thin wire transmits pressure forces to the axially movable sealingelement and the valve seat; and a restoring spring exhibiting an elasticforce for holding the axially movable sealing element in contact withthe valve seat, wherein the valve needle is formed by the thin wire, thethin wire including an elastic wire which is coupled to the restoringspring as a single piece.
 2. The fuel injection valve according to claim1, wherein the valve needle has a support element for increasing aflexural strength of the thin wire.
 3. The fuel injection valveaccording to claim 2, further comprising: at least one connectingbracket, wherein the support element includes an L-shaped sheet metalpart having a plurality of legs, the legs having a bend portion whichcooperates with the at least one connecting bracket for enclosing thethin wire in the bend portion.
 4. The fuel injection valve accordingclaims 1, wherein the thin wire is connected to the axially movablesealing element via a non-positive connection.
 5. The fuel injectionvalve according to claim 4, wherein the thin wire has a downstream endportion which has a rounded shape and which engages in a depression ofthe axially movable sealing element.
 6. The fuel injection valveaccording to claim 5, wherein the depression has a conical shape.
 7. Thefuel injection valve according to claim 1, further comprising: a flatarmature having a step portion, wherein the restoring spring contactsthe step portion of the flat armature.
 8. The fuel injection valveaccording to claim 1, wherein the axially movable sealing element has adisk shape.
 9. The fuel injection valve according to claim 8, furthercomprising: a valve seat body coupled to the axially movable sealingelement and having the valve seat; and an elastic corrugated diskdisposed between the axially movable sealing element and the valve seatbody, the corrugated disk exerting a force on the axially movablesealing element for lifting the axially movable sealing element from thevalve seat to be out of the closed position.
 10. The fuel injectionvalve according to claim 9, wherein at least one of the axially movablesealing element and the valve seat body is composed of a ceramicmaterial.
 11. The fuel injection valve according to claim 9, wherein thevalve seat body has a conical orifice, and further comprising: aself-centering perforated disk having, at least partially, a conicaldesign and being insertable into the conical orifice.
 12. The fuelinjection valve according to claim 11, wherein the self-centeringperforated disk is pressed against the valve seat body for securing theself-centering perforated disk in the fuel injection valve.